1. Field of the Invention
The present invention relates to communications networks and, more specifically, to quality-of-service (QoS) management for QoS-sensitive services in communications networks, such as voice-over-Internet protocol (VoIP) services.
2. Description of the Related Art
Circuit-switched networks, such as the public switched telephone network (PSTN), utilize signaling to establish call connections along a path between a call's source and its destination. Each call connection uses a time slot on each link in its path and each switch maps a call from an input port and/or time slot to an output port and/or time slot. The selection of time slots and mappings happens during the call setup signaling. Once a call is established, these slots are dedicated to the call so there is no contention for resources after the call is set up. In other words, quality of service (QoS) during a call is guaranteed by dedicating resources during the entire call. If no slot is available on any one of the links to support a new call, then the call request is denied. Thus, one measure of QoS for the PSTN is the probability of denying a call request, also known as the blocking probability. Another measure of QoS is the time to get the dial tone and post-dial delay for setting up the call. Other important elements of QoS, including bounds on delay, jitter, and loss, are a natural result of the dedicated nature of the connections in a circuit-switched architecture.
Packet networks, on the other hand, do not dedicate resources to a “connection” and are thus subject to contention among connections. Many packet networks use best-effort techniques to support data “connections” and they typically fail to provide QoS guarantees in terms of bounds on delay, jitter, and loss. However, the prevalence of packet networks, such as Internet Protocol (IP)-based Internet and Intranets, and the desire to utilize a common technology or suite of technologies for data as well as voice and other QoS-sensitive services, have led to a need for QoS guarantees within packet networks. Packet networks, in particular best-effort IP networks, inherently suffer from variable delay, jitter, and loss that may violate some QoS requirements of QoS-sensitive applications. Signaling in packet networks, when employed, might address the notification of connection failure or congestion, but the signaling does not address comprehensive QoS management and efficient utilization of resources in providing guaranteed QoS services. IP routers, for example, typically will not reject new bandwidth requirements levied upon them, even if the routers are burdened beyond the bandwidth capacities of one or more outgoing links. For example, when best-effort IP networks carry voice services, accepted calls can experience degradation in QoS or even failure, and the accepted calls can degrade other calls that were already in progress.